Bacteria and Butter-Making, 143 



specific organisms that were selected on account of their 

 ability to produce a desirable ripening change in cream. 

 The introduction of these so-called culture starters has be- 

 come almost universal in Denmark and in parts of Ger- 

 many. Their use is also extending in this country, Aus- 

 tralia and New Zealand. 



Principles of pure-culture cream-ripening:. In the proper 

 use of pure cultures for ripening cream, it is necessary first 

 to eliminate as far as possible the bacteria already present 

 in cream before the culture starter is added. This result is 

 accomplished by heating the cream to a temperature suf- 

 ficiently high to destroy the vegetating organisms. The 

 addition of a properly selected starter will then give the 

 chosen organism such an impetus as will generally enable 

 it to gain the ascendency over any other bacteria and so 

 control the character of the ripening. The principle em- 

 ployed is quite like that practiced in raising grain. The 

 farmer prepares his soil by plowing, in this way killing the 

 weeds. Then he sows his selected grain, which is merely a 

 pure culture, and by the rapid growth of this, other forms 

 are held in check. 



The attempt has been made to use these culture starters 

 in raw sweet cream, but it can scarcely be expected that 

 the most beneficial results will be attained in this way. 

 This method has been justified on the basis of the following 

 experiments. Where cream is pasteurized and no starter 

 is added, the spore-bearing forms frequently produce unde- 

 sirable flavors. These can almost always be controlled if 

 a culture starter is added, the obnoxious form being re- 

 pressed by the presence of the added starter. This condi- 

 tion is interpreted as indicating that the addition of a starter 

 to cream which already contains developing bacteria will 



